The invention described herein was made in the performance of official duties by employees of the Department of the Navy and may be manufactured, used, licensed by or for the Government for any governmental purpose without payment of any royalties thereon.
The invention relates generally to the measurement of water current, and more particularly to a method and system that provides for the non-invasive measurement of water current magnitude and direction.
A variety of small unmanned underwater vehicles are in development and use today. In situations where precision navigation is critical (e.g., mine clearing activities carried out by torpedo-like vehicles), surface and/or underwater currents can affect navigation performance and, therefore, affect the outcome of a vehicle""s mission. Accordingly, it would be beneficial to know what the surface and/or bulk underwater currents are prior to vehicle deployment in order to aid in selection of vehicle heading, speed, operating depth, etc. Ideally, measurement of surface and/or bulk underwater currents would be accomplished non-invasively (i.e., no measurement device need be placed in the water) from a remote location.
Accordingly, it is an object of the present invention to provide a method and system for measuring water currents in a body of water.
Another object of the present invention is to provide a non-invasive method and system for measuring water currents.
Yet another object of the present invention is to provide a method and system for remotely measuring underwater currents.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
In accordance with the present invention, a method and system are provided for measuring water current. A beam of radiation is transmitted so that it is incident at a target location on the surface of a body of water at an angle with respect to the surface. The beam is modulated by an acoustic frequency. As the beam transits the water, acoustic radiation propagates away from the beam with a portion thereof propagating to the surface. As the acoustic radiation propagates to the surface of the water, it experiences a Doppler shift in frequency relative to the acoustic frequency used to modulate the beam of radiation. The Doppler shift is caused by current in the water through which the acoustic radiation transits. The Doppler-shifted frequency is measured as an indication of water current.